Vehicle fuel economy can be improved for some vehicles by lowering the vehicle's engine displacement and by boosting the air supplied to the engine. The air may be boosted via a turbocharger compressor or via a mechanically driven super charger. Engine pumping work can be decreased by reducing engine displacement, and boosting the engine air supply can allow a smaller displacement engine to have performance similar to a larger displacement engine. However, when engine displacement is lowered and intake air pressure boosted, it may be difficult to provide vacuum to assist an operator to apply vehicle brakes. For example, since engine displacement is reduced, a smaller displacement engine may have to operate at higher intake manifold pressures for longer periods of time as compared to larger displacement engines. Consequently, the engine may operate for less time at operating conditions where the engine produces vacuum in the engine intake manifold. As a result, the amount of engine vacuum produced may be less than is desirable to operate vehicle brakes.
The inventors herein have recognized the issues of vacuum assisted brakes in boosted engines and have developed a method for improving brake operation of a vehicle, comprising: generating a positive pressurized air referenced to atmospheric pressure; applying the positive pressurized air to a first chamber of a brake booster; and actuating a vehicle brake via a brake booster diaphragm, the brake booster diaphragm exposed to the first chamber.
By applying a positive pressure to the first chamber of a brake booster it is possible to deflect a diaphragm of the brake booster so that it is possible to assist an operator applying vehicle brakes even though the engine may be operating at conditions where little engine vacuum is available to actuate vehicle brakes. For example, a portion of pressurized air entering an engine via a compressor can be directed to a brake booster to actuate vehicle brakes.
In another example, engine vacuum may be provided to one chamber of a brake booster while a positive pressure is applied to another chamber of the brake booster diaphragm so that the operator may be assisted by vacuum and positive pressure. A diaphragm between the first and second chambers may deflect in response to a pressure differential across the diaphragm. In these ways, it is possible to assist an operator applying brakes of a downsized boosted engine.
The present description may provide several advantages. In particular, the approach may enhance vehicle brake assistance by augmenting vacuum assistance with positive pressure assistance. Further, the approach may provide improved brake actuator assistance during engine operating conditions when brake actuator assistance may otherwise be reduced. Further still, the approach may be useful to reduce brake booster size since more force may be applied to the brake booster diaphragm.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.